Flexible blade fan

ABSTRACT

A screw type multiblade molded fan of plastic material comprising a central hub and a plurality of blades radially extending from said hub in an imaginary plane normal to the axis of rotation of the fan, each blade being integral with said hub and curved forwardly away from said plane characterized in that each blade decreases thickness thereof at the middle portion in cross sectional shape. A flexible trailing portion is provided in each blade by such formation of each blade to thereby decrease an inclination angle of each blade as the rotational speed of the fan is increased. The reduction of the angle is then decreases the air flow which thereby decreases the horsepower requirement and the fan noise as the rotational speed of the fan is increased.

United States Patent 1 Aiki et al.

[ Oct. 28, 1975 FLEXIBLE BLADE FAN [73] Assignee: Aisin Seiki KabushikiKaisha,

Kariya, Japan [22] Filed: Dec. 29, 1972 [21] Appl. No.: 319,860

[30] Foreign Application Priority Data Dec. 29, 1971 Japan 47-2956 [52]US. Cl 416/132; 416/240 [51] Int. Cl? F04D 29/38 [58] Field of Search416/132, 240, 241 A [56] References Cited UNITED STATES PATENTS1,798,299 3/1931 Antoni 416/240 3,054,355 9/1962 Neely 416/240 X3,584,969 6/1971 Aiki et al. 416/132 FOREIGN PATENTS OR APPLICATIONS2,013,481 10/1970 Germany 416/132 Primary Examiner Everette A. Powell,Jr. Attorney, Agent, or FirmWaters, Schwartz & Nissen [5 7] ABSTRACT Ascrew type multiblade molded fan of plastic material comprising acentral hub and a plurality of blades radially extending from said hubin an imaginary plane normal to the axis of rotation of the fan, eachblade being integral with said hub and curved forwardly away from saidplane characterized in that each blade decreases thickness thereof .atthe middle portion in cross sectional shape. A flexible trailing portionis provided in each blade by such formation of each blade to therebydecrease an inclination angle of each blade as the rotational speed ofthe fan is increased. The reduction of the angle is then decreases theair flow which thereby decreases the horsepower requirement and the fannoise as the rotational speed of the fan is increased.

3 Claims, 6 Drawing Figures US. Patent 'Oct.28,'1975 Sheet1of2 3,915,591

US. Patent Oct. 28, 1975 SheetZ of? 3,915,591

FIG.

FIG.

FLOW OF AIR PRODUCED FLEXIBLE BLADE FAN BACKGROUND OF THE INVENTION Thisinvention relates to multiblade molded plastic fans, and particularly toa fan of the flexible multiblade molded screw type.

The screw type multiblade fans which are employed on automotive vehicleengines are driven at a greater speed as the speed of the travellingvehicle is increased. This increases the horsepower requirement due tothe increase in air velocity.

While various means have been previously employed for a fan of theflexible multiblade molded screw type to decrease the horsepowerrequirement and the noise which would be increased if the flow of airwere increased, none have proven to be entirely sufficient.

SUMMARY OF THE INVENTION A principal object of the invention is toprovide an improved fan of the flexible multiblade molded plastic typeto decrease the horsepower requirement and the noise as the rotationalspeed of the fan increases.

The foregoing object and others are attained according to at least oneaspect of the present invention through the provision of a plurality offlexible molded plastic blades extending from a hub and integral withthe hub wherein thickness of each blade decreases in successive steps atthe middle portion in cross sectional shape to form a series of partialblades different from each other in thickness. Each of said blades maybe further provided with at its foot portion a recess so as to separatea trailing portion from the hub.

Thus, in the disclosed embodiments, there are comprised a central huband a plurality of blades radially extending from said hub in animaginary plane disposed normal to the axis of rotation of the fan, eachsaid blade being integral with said hub and curved forwardly away fromsaid plane characterized in that each said blade decreases thicknessthereof at the middle portion in cross sectional shape so as to form aseries of two or more partial blades different from each other inthickness, whereby a flexible trailing portion is provided to bedeflected in each said blade by centrifugal force and that of thecontact of the air as the rotational speed of the fan is increased. Forassistance of such deflection of the trailing portion, the fan may bebeneficially provided with a recess at the foot portion of each blade soas to have the trailing portion separated from the hub and render theremaining part of said blade a leading portion.

. BRIEF DESCRIPTION OF THE DRAWINGS Additional objects and the novelfeatures of this invention will become apparent from the descriptionwhich follows, taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 is a front view of a preferred embodiment of the invention,wherein however only a fan blade has been specifically represented andthe remaining blades have been shown only in their whole or partialgeneral configuration;

FIG. 2 is a cross section of a fan blade, in the section being takenalong the line II-II in FIG. 1 and in the direction of the arrow;

FIG. 3 is a cross sectional view of the embodiment of FIG. 2 in whichshown common function by additional symbols for convenience ofunderstanding;

FIG. 4 shows a graph showing flow of air relative to the rotationalspeed of the fan as compared with the flow of air of the conventionalfan; and

FIGS. 5(a) and 5(b) are cross sections of other embodiments according tothe present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring in detail to thedrawings, particularly to the form of the invention shown in the FIGS. 1to 5, the same comprises a hub 1 and a plurality of properly pitchedblades 2 integral therewith and extended radially therefrom. The saidhub and blades are formed of a suitable molded flexible plastic materialwhich is capable of production, especially, by the existing methods ofinjection molding.

The hub l is formed with a central opening 3 to provide means formounting on a shaft (not shown) driven by the known engine driving shaftthrough a band (not shown) in the known manner. About the opening 3, areprovided a suitable number of spaced holes 4 to provide means to rotatethe hub 1 together with the driven shaft. Each of the blades is reducedat its bottom portion as at 5 so that a trailing portion 6 is formedseparately from the hub and the remaining part of the blade is rendereda leading portion 8. The trailing portion 6 is deflected by centrifugalforce: and that of the contacting air as the rotational speed of the fanis increased. Thus, by selecting the proper :shape and curvature of theblade 2 and its resistance, namely cross sectional shape, to deflection,the air flow may be maintained substantially constant, thereby reducingthe horsepower requirement as the speed of rotation in the direction ofarrow A of the fans is increased.

A fan of this type will have special applications on an automotiveengine as a substantial flow of air is required when the engine isidling or driving the vehicle at low speed, which requirementprogressively reduces as the speed of the vehicle increases. If the sameamount of air is propelled by the blades of the fan at high speed asubstantial amount of horsepower is required, resulting in inefficientoperation of the vehicle. With the flexible blade type of fan as hereinillustrated and described, the increased speed will progressivelyflatten the blades 2 namely an inclination angel a in FIG. 2 is reducedto increasing degree of rotational speed of the fan. Thus when asubstantial amount of air is required at low speed, the blades willmaintain the initial form and produce a maximum flow of air. As thespeed increases requiring a less amount of air, the blades will flattenand produce a decrease in air flow which thereby decreases suchhorsepower requirement and the noise which would be increased if theflow of air were increased.

What has been thus far described is a flexible fan of previouslyprovided structure, as commonly used in automotive vehicles. The fan ofthe present invention is further characterized in that, means to flattenthe blade is better provided by combining two or more types of bladedifferent in thickness so that a cross section of the resultantcomplexed blade varies in successive steps to alternation of types ofblade. The fan may beneficially and additionally be provided inpractical use with a recess at the bottom of each blade as shown inFIGS. 1 and 2. If the leading portion 8 shown in FIG. 2 is combined withanother imaginary trailing portion 6' indicated in dot and dash line inFIG. 2, a full section of a single type of blade is obtained in theabsence of the proposal of the invention, while resulting another fullcross section of another single type of blade from combining thetrailing portion 6 with another imaginary leading portion 8' indicatedby the broken line in the view.

In operation, when the fan rotates in the direction indicated by thearrow A in FIG. 1 and as the speed of rotation of the fan increases, theaction of the centrifugal force and the pressure of the air on theflexible blades will cause the blades to flatten particularly againstthe foot portions to an increasing degree with an increase in speed. Acentrifugal force on the center of gravity M of the trailing portion 6is exerted as at CF. in FIG. 1, and let the arrow C.F. denote the amountof the force, and arrow P in FIG. 2 the pressure of the air on thetrailing portion 6. The centrifugal force and the pressure togetherserve to reduce the inclination angle a as the rotational speed of thefan increases so that the blades are flattened as hereinbelow describedin detail. The reduction of the angle a, namely flattening of the bladessubstantially reduces the air flow produced thereby and reduces thehorsepower requirement. This reduction in air flow maintains the fannoise at a minimum. The centrifugal force CF. is divided into ahorizontal component II.C. and vertical component V.C. as indicated inFIG. 1. The horizontal component BC. is further divided into peripheralcomponent RC. and normal component N.C. as shown in FIG. 3. The normalcomponent N.C. seves substantially to rotate or swing the blade 2 aboutthe axis X of the leading portion 8. The torque about the axis X isderived from the foregoing as l X N.C., while 1 being an arm defined bythe axis X and center of gravity M as will be seen in FIG. 3. Thepressure P of the air shown in FIG. 2 may be divided into a surfacecomponent SC. and normal component N.C'. The normal component N.C'. alsoserves to swing the blade about the axis X.

The above two normal components NC. and N.C'. together serve incooperation to swing the blade 2 or the trailing portion 6 about theaxis X in the direction indicated by the arrow B in FIG. 2 when the fanis rotated in the direction indicated by the arrow A in FIG. 1 and asincreases the rotational speed.

It has been found beneficial in decreasing the horsepower requirement asthe rotational speed is increased ously presented fan. In FIG. 4, thehigher reduction rate of the airflow of the present invention may benoted as compared with the previous fan as the speed of the fanincreases.

In FIGS. 5(a) and 5(b), there are shown two other different embodimentsin which two different type blades are combined together to form acomplexed cross section of blade in a manner such that any one of thecomponent blades is unsymmetrical relative to the axis of the othercomponent blade.

It should be noted that the surface of the resultant blade must besmoothly continued from one type blade to the other type blade formaintaining the irregular eddy current of air at a minimum in operation.

What is claimed is: y

1. A screw type multiblade molded fan of plastic material comprising acentral hub and a plurality of blades radially extending from said hubin an imaginary plane disposed normal to the axis of rotation of thefan, each blade being integral with said hub and curved forwardly awayfrom said plane, each blade decreasing in thickness at the middleportion of said blade and then increasing in thickness rearwardly ofsaid middle portion, at least one side of said blade being shaped toreduce said thickness at the middle portion, sections of the blade withdifferent thicknesses being interconnected by smooth continuous surfacecontours, each blade having at the foot portion thereof a recess so thata trailing portion of each blade is separated from said hub to therebydecrease the horsepower requirement and the fan noise as the rotationalspeed of the fan increases.

2. A screw type multiblade molded fan of plastic material of claim 1wherein said decrease of the thickness is on any one of said faces ofsaid blade.

3. A screw type multiblade molded fan of plastic material comprising acentral hub and a plurality of blades radially extending from said hubin an imaginary plane disposed normal to the axis of rotation of thefan, each blade being integral with said hub and curved forwardly awayfrom said plane, each blade decreasing in thickness at the middleportion of said blade, at least one side of said blade being shaped toreduce said thickness at the middle portion, sections of the blade withdifferent thicknesses being interconnected by smooth continuous surfacecontours, each blade having at the foot portion thereof a recess so thata trailing portion of each blade is separated from said hub to therebydecrease the horsepower requirement and the fan noise as the rotationalspeed of the fan increases, said decrease of the thickness of said bladebeing on both faces of the blade.

1. A screw type multiblade molded fan of plastic material comprising acentral hub and a plurality of blades radially extending from said hubin an imaginary plane disposed normal to the axis of rotation of thefan, each blade being integral with said hub and curved forwardly awayfrom said plane, each blade decreasing in thickness at the middleportion of said blade and then increasing in thickness rearwardly ofsaid middle portion, at least one side of said blade being shaped toreduce said thickness at the middle portion, sections of the blade withdifferent thicknesses being interconnected by smooth continuous surfacecontours, each blade having at the foot portion thereof a recess so thata trailing portion of each blade is separated from said hub to therebydecrease the horsepower requirement and the fan noise as the rotationalspeed of the fan increases.
 2. A screw type multiblade molded fan ofplastic material of claim 1 wherein said decrease of the thickness is onany one of said faces of said blade.
 3. A screw type multiblade moldedfan of plastic material comprising a central hub and a plurality ofblades radially extending from said hub in an imaginary plane disposednormal to the axis of rotation of the fan, each blade being integralwith said hub and curved forwardly away from said plane, each bladedecreasing in thickness at the middle portion of said blade, at leastone side of said blade being shaped to reduce said thickness at themiddle portion, sections of the blade with different thicknesses beinginterconnected by smooth continuous surface contours, each blade havingat the foot portion thereof a recess so that a trailing portion of eachblade is separated from said hub to thereby decrease the horsepowerrequirement and the fan noise as the rotational speed of the fanincreases, said decrease of the thickness of said blade being on bothfaces of the blade.